A very small number of PocketPCs are upgradable to WM 5. These upgrades are sold through the vendors directly (e.g. HP, Dell, etc.). Since you didn't provide any information about what model you have, that's all the help we can provide.

If you haven't heard of an upgrade for your device, chances are you really will have to buy a new PocketPC.

Jacob's right. The reason why WM5 is not available to the general public is because device makers have to customize the operating system to work with their hardware. Its similar to the PC, as each hardware needs a driver, only that these drivers has a common platform, a x86 CPU, video card, and slots whereas each PPC has its own hardware that are proprietary to the makers.

You can't just have the Windows OS, but hard setting it would do a "fresh" install. Also, if you are looking for custom ROMs, go to www.xda-developers.com and they might have something going. But as of now, the k-jam is too new for people to develop hacks on it.